Electro-chemical hardening of bearing raceways

ABSTRACT

A method of making bearings includes treating a metallic surface of a bearing raceway with a pulsed electrochemical processing nozzle to transform the amorphous oxide into a crystalline structure on the metallic surface electro-chemically and convert the metallic surface into a ceramic like hardness surface. Treating the metallic surface can include forming a gradient in material composition transitioning from a purely metallic material at a cross-sectional position within the bearing raceway to a purely crystalline structure material at the ceramic like hardness surface of the bearing raceway.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/515,900, filed Jun. 6, 2017, which is incorporated herein byreference in its entirety.

BACKGROUND Field of the Invention

The present disclosure relates to bearings, and more particularly to useof electro-chemical hardening of bearing raceways such as in aerospaceapplications.

Description of Related Art

Most bearings have steel outer and inner raceways, and steel rollingelements. Ceramics have been introduced into bearings for improving lifewith the harder ceramic material. Hybrid bearings have rolling elementswhich are ceramic and the raceways are steel, which when designedproperly will allow the steel raceway to deform and achieve full contacton the rolling element. However the life of the bearing is limited tothe life of the raceway.

The conventional techniques have been considered satisfactory for theirintended purpose. However, there is an ever present need for improvedbearings. This disclosure provides a solution for this need.

SUMMARY OF THE INVENTION

A method of making bearings includes treating a metallic surface of abearing raceway with a pulsed electrochemical processing nozzle totransform the amorphous oxide into a crystalline structure on themetallic surface electro-chemically and convert the metallic surfacehardness to an equivalent of diamond like or ceramic like hardness.

Treating the metallic surface can include forming a gradient in materialcomposition transitioning from a purely metallic material at across-sectional position within the bearing raceway to a purely ceramiclike hardness crystalline structure material at the surface of thebearing raceway. A gradient depth can be defined from thecross-sectional position where the gradient in material composition is apurely metallic material, to the purely ceramic like hardnesscrystalline structure surface, wherein the gradient depth is within arange up to 300 microns. Converting the metallic surface into a ceramiclike hardness crystalline structure surface can include hardening themetallic surface into a ceramic like hardness crystalline structuresurface with a hardness greater than or equal to a hardness of 80 on theRockwell hardness scale.

The bearing raceway can be an inner bearing raceway, wherein treatingthe metallic surface of the bearing raceway includes treating a radiallyoutward facing metallic surface of the inner raceway, and leaving aradially inward facing metallic surface of the inner raceway metallic.The method can include treating a metallic surface of an outer bearingraceway with an electro-chemical processing nozzle to transform theamorphous oxide into a crystalline structure on the metallic surface ofthe outer bearing raceway electro-chemically to convert the metallicsurface hardness to an equivalent of diamond like or ceramic likehardness, wherein treating the metallic surface of the outer bearingraceway includes treating a radially inward facing metallic surface ofthe outer raceway, and leaving a radially outward facing metallicsurface of the outer raceway metallic. The method can include assemblingthe inner and outer bearing raceways together with a plurality ofceramic rolling elements therebetween.

A bearing can be produced by processes as described above. For example,with an inner bearing race and outer bearing race as described aboveassembled together with a plurality of ceramic rolling elementstherebetween, the ceramic rolling elements can contact the inner andouter bearing races only on the ceramic like hardness crystallinestructure surfaces thereof.

These and other features of the systems and methods of the subjectdisclosure will become more readily apparent to those skilled in the artfrom the following detailed description of the preferred embodimentstaken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject disclosureappertains will readily understand how to make and use the devices andmethods of the subject disclosure without undue experimentation,preferred embodiments thereof will be described in detail herein belowwith reference to certain figures, wherein:

FIG. 1 is a perspective view of an exemplary embodiment of a bearingconstructed in accordance with the present disclosure, showing the innerand outer bearing raceways;

FIG. 2 is an exploded perspective view of the bearing of FIG. 1, showingthe treated surfaces of the inner and outer bearing races; and

FIG. 3 is a schematic cross-sectional elevation view of a portion of abearing race of FIG. 1, showing the material gradient transitioning frompurely metallic to purely ceramic like hardness crystalline structure atthe surface.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectdisclosure. For purposes of explanation and illustration, and notlimitation, a partial view of an exemplary embodiment of a bearing inaccordance with the disclosure is shown in FIG. 1 and is designatedgenerally by reference character 100. Other embodiments of bearings inaccordance with the disclosure, or aspects thereof, are provided inFIGS. 2-3, as will be described. The systems and methods describedherein can be used to improve surface hardness on bearing surfaces,while maintaining the ductility afforded by metallic materials underlingthe hardened surfaces.

Bearing 100 includes an outer bearing raceway 102 assembled togetherwith an inner bearing raceway 104 with a plurality of ceramic rollingelements 106 therebetween for relative rotational movement of the outerand inner bearing raceways 102 and 104. A cage 108 is also assembledonto the ceramic rolling elements 106 to maintain the ceramic rollingelements 106 in position. In FIG. 2, the cage 108 is shown split apartfor sake of clarity.

A method of making bearings such as bearing 100 includes treating aninitially metallic surface of a bearing raceway, e.g., bearing raceway102 or 104, with a pulsed electrochemical processing nozzle, e.g. nozzle110 shown in FIG. 2, to transform the amorphous oxide into a crystallinestructure on the metallic surface electro-chemically and convert themetallic surface, which initially had a metallic surface hardness, tohave a diamond like or ceramic like hardness crystalline structuresurface.

In FIG. 2, nozzle 110 is schematically shown electrochemicallyprocessing the radially outer surface 112 of inner bearing raceway 104,which is initially a metallic surface, into a ceramic like hardnesscrystalline structure surface. This leaves a radially inward facingmetallic surface 118 of the inner raceway 104 metallic. Similarly, themethod can include treating a metallic, radially inward facing surface114 of the outer bearing raceway 102 with the electro-chemicalprocessing nozzle 110 to transform the amorphous oxide into acrystalline structure on the initially metallic surface 114 of the outerbearing raceway electro-chemically to convert the initially metallicsurface 114 into a ceramic like hardness crystalline structure surface,and leaving a radially outward facing metallic surface 120 of the outerraceway 102 metallic. After the surfaces 112 and 114 have been treatedas described above, the inner and outer bearing raceways 102 and 104 canbe assembled together with the plurality of ceramic rolling elements 106therebetween to form a functional bearing 100. The ceramic rollingelements 106 can advantageously contact the inner and outer bearingraces only on the ceramic like hardness crystalline structure surfaces112 and 114 thereof.

With reference to FIG. 3, treating the metallic surface includes forminga gradient in material composition transitioning from a purely metallicmaterial at a cross-sectional position 116 within the bearing raceway102 or 104 to a purely ceramic like hardness crystalline structurematerial at the surface 112 or 114 of the bearing raceway 102 or 104,respectively. A gradient depth D can be defined from the cross-sectionalposition 116 where the gradient in material composition is a purelymetallic material, to the purely ceramic like hardness crystallinestructure surface 112 or 114, wherein the gradient depth D is within arange of up to 300 microns. Converting the metallic surface into aceramic like hardness crystalline structure surface can includehardening the metallic surface into a ceramic like hardness crystallinestructure surface with a resulting hardness greater than or equal to ahardness of 80 on the Rockwell hardness scale. Examples of metallicmaterials that can be used for raceways 102 and 104 include but are notlimited to M50, M50NIL, AISI 4320, AISI 4620, SAE 9310, SAE 52100, SAE8620, Cronidor, CSS 42L, and the like. The ceramic like hardnesscrystalline structure material can be or can be like silicon nitrideSi₃N₄, for example.

During the process of transforming the metallic material to a ceramiclike hardness material, the following can be used to determine when theprocess is complete. After setting up the chemical hardening process,the conversion of metal to metal oxide can begin. Plasma transformsamorphous oxide into a crystalline structure. Then a test can beperformed to determine whether power supplied results in continuousgrowth into the metallic material. If yes, then the process ofconverting metal to metal oxide, plasma transforming the amorphousoxide, and testing if the power supplied results in continuous growthcan be continued. Once the power supplied does not result in continuousgrowth into the metallic material, the process is complete.

Processes as described herein provide a metal and transforms theamorphous oxide into a crystalline structure on the surface that has theproperties of ceramic like hardness, e.g., high surface hardness, butthe flexibility or ductility/elasticity of metal. Using such surfacecrystalline structure with ceramic like hardness on metallic bearingraceways can extend the life of a bearing with beyond that ofconventional hybrid ceramic/metallic bearings. Bearings with surfacecrystalline structure with ceramic like hardness and metallic racewayscombined with ceramic rolling elements as disclosed herein can improvethe bearing loading and/or reduce the overall bearing size relative toconventional bearings. This can have a considerable impact in gearboxdesign configurations that have a pinion bearing that is highly loaded,but is restricted in size to avoid interference with the mating gear,for example. With surface crystalline structure with ceramic likehardness and metallic raceways, bearings can be designed with unlimitedor improved life compared to traditional techniques.

The methods and systems of the present disclosure, as described aboveand shown in the drawings, provide for bearings with superior propertiesincluding improved surface hardness and mechanical flexibility forimproved life relative to conventional bearings. While the apparatus andmethods of the subject disclosure have been shown and described withreference to preferred embodiments, those skilled in the art willreadily appreciate that changes and/or modifications may be made theretowithout departing from the scope of the subject disclosure.

What is claimed is:
 1. A method of making bearings comprising a bearingraceway rotatably housing a plurality of ceramic rolling elements, themethod comprising: treating a metallic surface of the bearing racewaywith a pulsed electrochemical processing nozzle to transform amorphousoxide into a crystalline structure on the metallic surfaceelectro-chemically and convert the metallic surface into a ceramic likehardness crystalline structure surface.
 2. The method as recited inclaim 1, wherein treating the metallic surface includes forming agradient in material composition transitioning from a purely metallicmaterial at a cross-sectional position within the bearing raceway to apurely ceramic like hardness crystalline structure material at thesurface of the bearing raceway.
 3. The method as recited in claim 2,wherein a gradient depth is defined from the cross-sectional positionwhere the gradient in material composition is a purely metallicmaterial, to the purely ceramic like hardness crystalline structuresurface, wherein the gradient depth is within a range up to 300 microns.4. The method as recited in claim 1, wherein treating the metallicsurface of the bearing raceway includes treating a radially outwardfacing metallic surface of an inner raceway, and leaving a radiallyinward facing metallic surface of the inner raceway metallic.
 5. Themethod as recited in claim 1, wherein treating the metallic surface ofthe bearing raceway includes treating a radially inward facing metallicsurface of an outer raceway, and leaving a radially outward facingmetallic surface of the inner raceway metallic.
 6. The method as recitedin claim 1, wherein the bearing raceway is an inner bearing raceway,wherein treating the metallic surface of the bearing raceway includestreating a radially outward facing metallic surface of the innerraceway, and leaving a radially inward facing metallic surface of theinner raceway metallic, and further comprising: treating a metallicsurface of an outer bearing raceway with an electro-chemical processingnozzle to transform amorphous oxide into a crystalline structure on themetallic surface of the outer bearing raceway electro-chemically toconvert the metallic surface into a ceramic like hardness crystallinestructure surface, wherein treating the metallic surface of the outerbearing raceway includes treating a radially inward facing metallicsurface of the outer raceway, and leaving a radially outward facingmetallic surface of the inner raceway metallic; and assembling the innerand outer bearing raceways together with a plurality of ceramic rollingelements therebetween.
 7. The method as recited in claim 1, whereinconverting the metallic surface into a ceramic like hardness crystallinestructure surface includes hardening the metallic surface into a ceramiclike hardness crystalline structure surface with a hardness greater thanor equal to a hardness of 80 on the Rockwell hardness scale.
 8. Abearing comprising: a bearing raceway including a raceway with a ceramiclike hardness crystalline structure surface over a purely metallicmaterial; and ceramic rolling elements disposed at the ceramic likehardness crystalline structure surface.
 9. The bearing as recited inclaim 8, wherein the bearing raceway includes a gradient in materialcomposition transitioning from a purely metallic material at across-sectional position within the bearing raceway to a purely ceramiclike hardness crystalline structure material at the surface of thebearing raceway.
 10. The bearing as recited in claim 9, wherein agradient depth is defined from the cross-sectional position where thegradient in material composition is a purely metallic material, to thepurely ceramic like hardness crystalline structure surface, wherein thegradient depth is within a range up to 300 microns.
 11. The bearing asrecited in claim 8, wherein the ceramic like hardness crystallinestructure material is on a radially outward facing surface of an innerraceway, with a radially inward facing metallic surface of the innerraceway being metallic.
 12. The bearing as recited in claim 8, whereinthe ceramic like hardness crystalline structure material is on aradially inward facing metallic surface of an outer raceway, with aradially outward facing metallic surface of the outer raceway beingmetallic.
 13. The bearing as recited in claim 8, wherein the bearingraceway is an inner bearing raceway, wherein the ceramic like hardnesscrystalline structure material is on a radially outward facing metallicsurface of the inner raceway, with a radially inward facing metallicsurface of the inner raceway being metallic, and further comprising: anouter bearing raceway with a ceramic like hardness structure material onthe a radially inward facing surface of the outer bearing raceway, witha radially outward facing surface of the outer raceway being metallic;and wherein the inner and outer bearing raceways are assembled togetherwith a plurality of ceramic rolling elements therebetween.
 14. Thebearing as recited in claim 13, wherein the ceramic rolling elementsonly contact the inner and outer bearing races on the ceramic likehardness crystalline structure surfaces thereof.
 15. The bearing asrecited in claim 8, wherein the ceramic like hardness surface has ahardness greater than or equal to a hardness of 80 on the Rockwellhardness scale.
 16. The bearing as recited in claim 8, wherein thebearing raceway is produced by a process including treating a metallicsurface of a bearing raceway with an electro-chemical processing nozzleto transform amorphous oxide into a ceramic like hardness crystallinestructure on the metallic surface electro-chemically to convert themetallic surface into a ceramic like hardness crystalline structuresurface.